Missing beforedepend dependencies for Menhir

Ensures that Menhir's sources are in place for a "from scratch"
`make alldepend`

Makefile

@@ -1074,6 +1074,9 @@ parsing/parser.ml: boot/menhir/parser.ml parsing/parser.mly \
 parsing/parser.mli: boot/menhir/parser.mli
 	cat $< | sed "s/MenhirLib/CamlinternalMenhirLib/g" > $@
 
+beforedepend:: parsing/camlinternalMenhirLib.ml \
+  parsing/camlinternalMenhirLib.mli \
+	parsing/parser.ml parsing/parser.mli
 
 partialclean:: partialclean-menhir